I want my grilfriend to "cheat" on me

I have suggested to my girlfriend of 3 years to have s** with other men I am the only one she has been with. I have been with others before her and I see it as fair. I want her to be happy and explore and am totally ok with her doing anything she wishes with them. she is kind of shaky on the idea. any suggestions as to how to make her more comfortable with it?